[sdiy] Retarded function generator - Agilent 33220A

[jays at aracnet.com]

Charles,

I'm pretty familar with the 33220A. On a daily basis I have a hate relationship with one on my desk. If I were looking for a signal generator I would avoid this one. Granted some of my problems with the unit are with the GPIB/PI implementation which most people here wouldn't use.
1) Soft knob crapped out a month out of warrenty. Costs about 1K to fix.
2) The only reliable way I can control it externally is with the GPIB interface. The network and USB interfaces are marginal.
3) Some important features can not be controlled over the GPIB/PI interface and have to manually be tweaked.
4) Some of the waveforms aren't as good as they should be.

There probably is a very simple explination why this happens. Check the termination of the 33220A which is at Utility | Output Setup | Load. Switching between 50 ohm and hi-z termination screws with the output level. Having it set to 50 ohms with 10V output and driving a hi-z input will probaly give you about 20V out. That or just changing the termination can change the output voltage. This is not a unique feature for this signal generator. There are a number of other ones that do this also.

Jay S.


Charles Bisaillon wrote:

> Hi, I would love to get your opinion on this one,
> 
> I remember having unexpected low level problems when we were presenting the
> capstone modular project. Well, I recently learned from a classmate that the
> function generator I used to design the whole synth actually outputs twice
> the voltage selected. I remember setting it daily to 10Vpp and using it
> instead of my 10Vpp VCO. I went back to check verify this and he was right,
> set at 10Vpp, I get 20Vpp at the output. How can someone design such a
> stoopid thing?
> 
> Anyways, this means that all of my module's inputs, unity gain, clip
> circuitry, headroom, etc, are designed to receive twice the voltage that
> they will operate on. On the other hand, all my outputs are designed
> properly and yield proper levels (provided you get a proper input, which in
> this case is 20Vpp). It's such a pain, even my 1V/oct is actually designed
> for 2V/oct...
> 
> I now have a choice to make: Raise the VCO outputs to 20Vpp instead of 10Vpp
> and the ADSR to 10V instead of 5V, or go back to the breadboard and redesign
> the VCF and VCA? I would love to get your opinions on this.
> 
> Thanks
> 
> Charles (I hate electronics)
> 
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